Grease 4 heat-proof silicone muffin cups (or form 4 cups from heavy-duty foil, each about 3 inches wide and 2 inches deep) with butter or oil. Set aside.

In a mixing bowl, whisk together eggs, milk, salt, and pepper until uniform and slightly frothy, about 30 seconds.

Stir in cheese, bell pepper, and onion until evenly distributed.

Place your cast iron skillet on the camp stove or campfire grate over medium heat. Add a splash of water to the skillet (about 1/4 cup) to create gentle steam — this is key for fluffy egg bites without burning.

Carefully place the greased muffin cups into the skillet. Pour the egg mixture evenly into the cups, filling each about 3/4 full.

Cover the skillet with a lid or a sheet of foil. Cook over medium-low heat (or over coals that are not directly flaming) for 15-20 minutes. The water in the skillet should be gently steaming, not boiling hard.

Check at 15 minutes: the egg bites are done when the centers are just set — a knife inserted into the center comes out clean or with a few moist crumbs. If the top still looks wet, cover and cook 2-3 more minutes.

Use a spatula to lift the cups out of the skillet. Let cool 2 minutes in the cups, then pop the egg bites out. Serve warm or at room temperature.